Method for depositing glass particles on the entire exposed surface of an object



April 8, 1969 B. NARKEN ETAL 3,437,505

' METHOD FOR DEPOSITING GLASS PARTICLES ON THE ENTIRE EXPOSED SURFACE OF AN OBJECT Filed June 28, 1965 IN VEN TOR. BERNT NARKEN HOWARD L. WHITAKER ATTORNEY United States Patent Ofice US. Cl. 117-23 6 Claims ABSTRACT OF THE DISCLOSURE A method for forming a thin, hole-free, glass film on the entire surface of an object which may be irregular in shape. The object to be coated is suspended in a container above a deposit of glass particles, micron size, in the bottom of the container. The object is heated and a gas under pressure is directed against the deposit of glass particles to raise a cloud of particles surrounding the heated object. Particles from the cloud contact the surface and fuse to form the thin, hole-free film.

This invention is directed generally to a method and apparatus for depositing particles onto an object and, more particularly, to a method and apparatus for depositing micron size glass particles onto an dbject and subsequently forming a thin, hole-free, glass film thereon.

It is often desirable to deposit particles of a particular substance onto an object to create a new or improved product which has enhanced qualities. In manufacturing cathode ray tubes, for example, it is often desirable to form the screen by depositing fluorescing powdered material sensitive to electron beam bombardment on the face of a cathode ray tube. The deposited powdered material is generally deposited with a binder substance to adhere the powdered material to the face of the cathode ray tube, however, the binder material can be applied to the powdered material after its deposition on the face of the cathode ray tube.

In many situations it is desirable to deposit particles onto an object and fuse or join the deposited particles to form a coating on or about the object. In the manufacture of various electronic components such as resistors, capacitors, memory elements, and semiconductor devices, it is often necessary to provide a tightly adherent protective jacket which serves as a hermetic seal and prevents the contamination of the components by foreign or noxious materials which may impair the electrical characteristics of the device or may physically damage them so as to render them unsatisfactory or worthless. A wide variety of coating materials sudh as plastic and glass have been employed with some success and some of these coating materials have been formed by fusing or joining particles deposited on the components.

The present trend in the electronic computer fields is toward the miniaturization of semiconductor or solid state components, i.e., integrated or monolithic circuits. Accordingly, only thin protective coatings are practical since thick protective coatings undesirably increase the bulk of such components and often such thick jackets are subject to cracking during use over a range of operating temperatures.

Two US. patent applications entitled Method of Forming a Glass Film on an Object and the Product Produced Thereby and Method of Forming a Glass Film on an Object, whose respective serial numbers and filing dates are S.N. 141,668 and S.N. 181,743, filed Sept. 29, 1961, and Mar. 22, 1962, now Patents Nos. 3,212,921

3,437,505 Patented Apr. 8, 1969 and 3,212,929 respectively, and assigned to the same assignee of this invention, relate to techniques for forming thin glass films on an object for the purpose of providing a hermetic seal or coating therefor. Both of these above-identified applications use centrifuging techniques for depositing glass particles onto the object and a glass film is then formed on the object by fusing or joining the deposited glass particles.

The difficulty with centrifuging techniques for depositing small size particles onto an object is that the deposited glass particles and the subsequent glass film that was formed on the object could only be formed on one surface of the object. Consequently, the centrifuging techniques that were previously used to deposit glass particles onto an object and the subsequent heat treatment of the object to form a glass film thereon were not applicable in forming glass films on the entire surface of an object that had crevices, cracks, or was irregularly shaped. Electronic components such as memory elements that are formed like the links of a chain otherwise known as chain store memories needed to be protected by an insulating glass layer that had to be formed on the entire irregular surface of the chain which was impossible to do with prior centrifuging techniques due to the irregular configuration of the object.

It has been known that fluidized beds could be used for coating an object with particles. The fluidized bed technique utilized a gas source which was directed at one side of a porous partition to form the fluidized bed on the other side of the partition. However, in depositing on an object very small particles, whose sizes are in the range of .01 to 1 micron, the fluidized bed technique could not be used due to the problem of raising these small size particles. The porous partition had to have openings smaller than the size of the particles so that the particles would not fall through and yet the openings in the porous partition had to be large enough to permit the passage therethrough of a gaseous fluid. The one micron or smaller size particles were too small to be raised or supported by the flow of a gas fluid through a porous partition located at the bottom of a container holding the particles. Consequently, a new approach was needed for depositing very small size particles onto irregular shaped objects.

Accordingly, it is an object of this invention, therefore, to produce a new and improved method for depositing particles onto an object.

It is another object of this invention to deposit particles on the entire surface of an irregularly shaped object.

It is still another object of this invention to provide an improved method for depositing glass particles onto an object and forming a glass film thereon.

It is a still further object of this invention to provide an improved method for forming a glass film on an irregularly shaped object.

It is another object of this invention to provide an improved apparatus for depositing small size particles onto the entire surface of an irregular shaped object.

It is a further object of this invention to provide an improved apparatus for depositing small size glass particles onto the entire surface of an irregularly shaped object for the purpose of producing a hermetically sealed, glass coating that would prevent contamination of the object.

In accordance with a particular form of the invention, the method of depositing micron size particles onto an object comprises placing the micron size particles at the bottom of a container. The size of the particles coated preferably range from .01 to 1 micron. A gas fluid is directed at the bottom of the container thereby forming a cloud of the micron size particles for deposition on the entire surface of an object located above the bottom of the container. In forming a thin, hole-free, glass film on the entire surface of an irregular shaped object, the micron size particles are made of a suitable glass material for forming an encapsulating glass film on the object. The object is heated preferably during particle deposition so as to fuse or join the deposited glass particles into a thin, hole-free, glass film.

Also in accordance with the invention there is provided an apparatus for depositing micron size. particles onto an object which includes a container having a layer of micron size particles, preferably, located at the bottom of the container. The article to be coated with the particles is, preferably, suspended above the bottom of the container. Fluid means are provided, which are located within the container, for forming a cloud of the micron size particles for deposition on the surface of the object. In the preferred embodiment, the fluid 'means consist of a conduit having one end spaced from the bottom of the container and a source of gas fluid within the conduit and adapted to be directed at the bottom of the. container through the one end of the conduit. Means are also provided for maintaining the layer of micron size particles at a uniform thickness thereby permitting increased particle deposition on the object. In forming a thin, holefree, glass film on the entire surface of the object which can be irregularly shaped, the micron size particles are made of a suitable glass material and means are provided for heating the object during particle deposition so as to fuse or join the deposited glass particles into a thin, holefree, glass film.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawmg.

In the drawing:

The sole figure is an elevational view partly in section showing an apparatus for depositing particles onto an irregularly shaped object.

In practicing the present invention with respect to depositing glass particles onto an object, a suitable glass is comminuted as by ball milling to form a powdered glass. Many different types of glasses are suitable for use in accordance with the method of the present invention. The type of glass selected may depend upon the particular application at hand. For example, the object to receive a thin, hole-free, glass film of uniform thickness may require a chemical resistive glass such as bore-silicate type glass for protective purposes and for withstanding high operating temperatures. Also, the object may be a semiconductor device such as a transistor which may dictate that, for protective purposes, the coeflicient of thermal expansion of the semiconductor material of the device and that of the glass film be substantially equal so as to minimize stresses which might otherwise crack the glass during temperature cycling. For example, silicon has a coeflicient of expansion per degree centigrade of 32x10, which is closely matched by that of a borosilicate glass available to the trade as Corning 7740 or Pyrex and having a coefficient of expansion of 32.6 The ball milling operation produces small particles of glass of varying size. Smaller size glass particles as small as 0.01 micron are produced by centrifuging techniques in accordance with the teachings of the two above-identified copending patent applications.

The glass particles were passed through a 325 mesh filter and the resulting distribution was such that approximately ten percent of the glass particles had sizes less than one micron with the remaining glass particles having sizes between one and 10 microns. Subsequently, approximately 25 grams of the glass powder was put in the bottom of a bell jar 10 to form a layer 12. The bell jar 10 is preferably of glass or any other suitable transparent material affording visual inspection within the container or bell jar 10 which helps in regulating the subsequent glass cloud formation to obtain optimum coating. In one example, the bell jar 10 was approximately 6 inches in diameter and 9 inches high. A cap 14 is threadedly con nected to the top of the of the bell jar 10 after a suitable flexible O-ring 16 is mounted on flange surface. 17 of the bell jar 10. The O-ring 16 is compressed by the cap 14 upon the tightening thereof to the top of the bell jar 10 thereby providing a hermetic seal between the cap -14 and the bell jar 10. An elongated tube 18, preferably of glass, having a diameter of approximately of an inch is inserted, through an opening in the cap 14, into the bell jar 10 to a position where one end of the tube 18 is immersed in the layer of glass particles 12. A suitable gas source (not shown) is connected to the other end of the conduit or glass tube 18 for pumping a gas fluid into the bell jar 10. Any suitable gas fluid can be used which will not chemically react with the glass particles 12. In one example, the gas fluid used was nitrogen which was pumped into the container at a rate of about two to three liters per minute thereby raising a cloud 19 composed of glass particles. Supported, preferably, at the upper portion of the bell jar 10 is an object 20 upon which the glass particles are deposited. The object 20 can be a semiconductor device upon which a glass film is to be formed or it can also be a memory device such as the chain store memory which is in the form of a fine, conventional, chain type configuration that has been flattened to a thickness of 2.5 mils and has a width of about 25 mils. In one example, the object 20 was made of a piece of beryllium copper that was two inches long. The object 20 was electrically heated by an electrical energy source 22 such as a Variac that was electrically connected to a pair of metal pinch clips 24 holding the object 20.

The power source 22 is used to electrically heat up the object 20 to a temperature about the melting temperature of the glass particles thereby causing the glass particles deposited on the object 20 to melt and fuse together to form a thin, hole-free, uniform glass film. This thin uniform glass film is formed on the entire surface of the irregular shaped object 20. In one example, a one mil glass coating was formed on the object 20 in approximately three minutes by means of the electrical heating of the object 20 with a small current of about 15 milliamps after the formation of the glass cloud 19. If the cap 14 is made of metal then short, cylinder sections 26 are formed of a suitable dielectric material for insertion within apertures in the cap 14. Preferably a flexible cap 14 is used and the cylinder sections 26 are made of any suitable material. The flexible cap 14 permits manipulation of the tube 18 as desired during the cloud formation operation.

Due to the location of the object 20 in the upper portion of the bell jar 10 only the smallest particles from the layer of micron size particles 12 were deposited on the object 20. In one example, the deposited particles had sizes in the range of 0.01 to 1 micron thereby providing a very fine, hole-free, glass film. After the cloud was maintained for about three minutes, the glass particles were allowed to settle to the bottom or were flushed out through an exit hole in the cap 14 before cooling the object 20. This permits producing a smooth glass film without having particles still on the surface in process of fusing. Accordingly in this manner, the entire surface of the object 20 was coated, completely and evenly, around all corners and on the inside surfaces and crevices without any flaws or cracks in the glass coating.

A conduit or tube 28 having one end communicating with the interior of the bell jar 10 is inserted through an opening in the cap 14. The function of tube 28 is to permit exhaust of the gas that is being supplied to the bell jar 10 through the conduit 18. An exhaust tank (not shown) can be connected to the end of the tube 28 that extends outside the bell jar 10.

If it is desirable to maintain a uniform thickness for the layer 12 of glass particles, a vibrating table 30 or any other vibration means is used to insure that the thickness of the layer 12 will be uniformly maintained during the cloud formation process. During the application of a gas fluid through the tube 18, the glass particles in the layer 12 located adjacent the end of the tube 18 are blown away creating a hole and the vibrations from the plate or table 30 cause the glass particles on the sides of the hole to fill the hole thereby permitting increased particle deposition on the object 20. The vibrating frequency of the vibration means used is selected as desired to maintain uniform layer thickness.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method for forming a thin, hole-free, glass film on the entire exposed surface of an object comprising the steps of:

placing micron size glass particles at the bottom of a container;

mounting said object above said micron size glass particles;

directing a gas fluid at the bottom of said container thereby forming a cloud of said micron size glass particles about said object, and depositing glass particles on said object; and

heating said object for a period of time and at a temperature sufiicient to fuse said deposited glass particles into a thin, hole-free, glass film.

2. The method of claim 1 wherein the object is heated simultaneously with the deposition of the glass particles.

3. A method for forming a thin, hole-free, glass film on the entire exposed surface of an object comprising the steps of:

placing micron size glass particles at the bottom of a container;

mounting said object above said micron size glass particles;

placing a conduit into said container with one end adjacent the bottom of said container;

directing a gas fluid through said conduit at the bottom of said container thereby forming a cloud of said micron size particles about said object, and depositing glass particles on said object; and

heating said object for a period of time and at a temperautre sufiicient to fuse said deposited glass particles into a thin, hole-free, glass film.

4. A method as in claim 3, wherein said object is an irregular shaped object.

5. A method for forming a thin, hole-free, glass film on the entire exposed surface of an irregular shaped object comprising the steps of:

placing a layer of micron size glass particles at the bottom of a container;

mounting said object above said layer of micron size glass particles;

placing a tube into said container with one end being disposed within said layer of micron size glass particles;

directing a gas fluid through said tube at said particles located at the bottom of said container thereby forming a cloud of said micron size glass particles about said object, and depositing glass particles on the entire surface of said object;

vibrating said container to maintain said layer of micron size glass particles at a uniform thickness; and

heating said object for a period of time and at a temperature sufficient to fuse said deposited glass par ticles into a thin, hole-free, glass film.

6. A method for forming a thin, hole-free, glass film on the entire exposed surface of an irregular shaped object comprising the steps of:

placing a layer of glass particles having sizes in the range of .01 micron to 10 microns at the bottom of a container;

mounting said object within said container and above said layer of glass particles; placing a tube into said container with one end being disposed Within said layer of glass particles;

directing a gas fluid through said tube at said particles located at the bottom of said container thereby forming a cloud of said glass particles about said object, and depositing glass particles on the entire surface of said object;

vibrating said container to maintain said layer of glass particles at a uniform thickness; and

applying an electric current to said object to heat it for a period of time and at a temperature sufficient to fuse said deposited glass particles into a thin, hole-free, glass film.

References Cited UNITED STATES PATENTS 2,803,559 8/1957 Rutherford et al. 11722X 3,032,816 5/1962 Zimmerli 117-18 X 3,037,885 6/1962 Abolins 118309 X 3,093,510 6/1963 Olson et al. 117-21 X 3,212,921 10/1965 Plisken et a1 117-201 X 3,212,929 10/1965 Plisken et a1 117201 WILLIAM D. MARTIN, Primary Examiner. PAUL ATTAGUILE, Assistant Examiner.

U.S. C1. X.R. 117-51; 118309 

